“On-demand” online services are increasingly common and present on multiple media, such as personal computers, television decoders connected to the Internet, mobile phones or tablets.
But these services need to be protected against users or malware seeking to illicitly exploit the data provided by these services, in particular in the field of on-demand videos or pay television.
Technical protection measures are therefore implemented to control the use made of digital works. For example, a Conditional Access System (CAS) is generally set up as part of a broadcast of video and audio content, or multimedia content.
In a CAS process, the multimedia content is encrypted by servers thanks to a symmetric key and the broadcast content is accessible only to clients holding said key.
On the other hand, notably in the context of downloading a data stream (“Streaming”) or a massive download of data, Digital Rights Management (DRM) systems are deployed.
In a DRM process, a client sends a server an identification key which is specific to it. If this client is authorized to access the content, the server encodes a content key thanks to the identification key and transmits the encoded content key to the authorized client which is the only one able to decode it. The encrypted multimedia content is then transmitted to the client which can decrypt it thanks to the decoded content key.
The encryption-decryption processes are implemented by encryption-decryption means, generally formed by autonomous and secure hardware blocks. The encryption-decryption means are controlled and managed by Digital Rights Management DRM means and Conditional Access CAS means, subsequently referred to as “DRM/CAS means”.
The DRM/CAS means may be implemented in a secure area (TEE for “Trusted Execution Environment”) of a computing system of the electronic medium, which is generally the main processor.
The TEE makes it possible notably to reliably execute secure software, termed reliable applications, by having a computing capacity and an average allocated secure memory. Computing systems generally comprise a physically secure element (SE for Secure Element) with little computing capacity but excellent security. Conversely, computing systems comprise an area allocated to an operating system (REE, for “Rich Execution Environment”) with large resources but little security and therefore very exposed to outside attacks.
On the other hand, protection for multimedia output interfaces has been developed, and is notably required by the services of multimedia content providers. For example, a version of HDCP protection may be required on an HDMI or DVI digital video and audio output interface.
Protection for analog video and audio outputs also exists, such as CGMS-A or “Macrovision”. Transcoding protection may be required, notably the DTCP protocol in WiFi wireless communication. Digital watermarking protection may further be required, consisting in incorporating in the multimedia content a mark invisible to human beings but traceable by machine.
The application of the multimedia output interface protection required and the delivery of a multimedia signal on a multimedia output interface are generally controlled by respective drivers from the REE.
The means for implementing said multimedia output interface protection, termed the protection means, and the delivery means, termed the multimedia output interface, are generally formed by autonomous and secure hardware blocks.
Faced with the diversification of media able to benefit from multimedia services protected by CAS and DRM, and therefore with the diversification of risks of fraud, it is desirable that electronic systems on chips (SoC for “System on Chip”) that implement these services are robust to malicious attacks, notably regarding multimedia interface protection.
In this regard, it might be possible to migrate the control and engagement of outgoing multimedia interface protection into a TEE secure zone. But this requires that the TEE has a sufficiently large computing capacity for directly controlling the multimedia interface protection, and migration of such systems is very demanding technologically. Indeed, many existing hardware blocks, each providing a function established and designed in a given technological sector, would undergo heavy modifications or even new designs.
To overcome these constraints, simple embodiments and implementations of enhancing the protection of a signal against a malicious attack are provided, for example, in multimedia device audio/video outputs, by monitoring the state of this signal, for example, the state of a multimedia output interface protection, and by exercising a “punitive” action if the signal exhibits an irregularity, for example, if the multimedia output interfaces are not properly protected.
A punitive action is, for example, a protective action for neutralizing or nullifying such a malicious attack on the signal.